Circulating tumor DNA analysis of the phase III VOYAGER trial: KIT mutational landscape and outcomes in patients with advanced gastrointestinal stromal tumor treated with avapritinib or regorafenib

BACKGROUND

The current treatment paradigm of imatinib-resistant metastatic gastrointestinal stromal tumor (GIST) does not incorporate KIT/PDGFRA genotypes in therapeutic drug sequencing, except for PDGFRA exon 18-mutant GIST that is indicated for avapritinib treatment. Here, circulating tumor DNA (ctDNA) sequencing was used to analyze plasma samples prospectively collected in the phase III VOYAGER trial to understand how the KIT/PDGFRA mutational landscape contributes to tyrosine kinase inhibitor (TKI) resistance and to determine its clinical validity and utility.

PATIENTS AND METHODS

VOYAGER (N = 476) compared avapritinib with regorafenib in patients with KIT/PDGFRA-mutant GIST previously treated with imatinib and one or two additional TKIs (NCT03465722). KIT/PDGFRA ctDNA mutation profiling of plasma samples at baseline and end of treatment was assessed with 74-gene Guardant360® CDx. Molecular subgroups were determined and correlated with outcomes.

RESULTS

A total of 386/476 patients with KIT/PDGFRA-mutant tumors underwent baseline (pre-trial treatment) ctDNA analysis; 196 received avapritinib and 190 received regorafenib. KIT and PDGFRA mutations were detected in 75.1% and 5.4%, respectively. KIT resistance mutations were found in the activation loop (A-loop; 80.4%) and ATP-binding pocket (ATP-BP; 40.8%); 23.4% had both. An average of 2.6 KIT mutations were detected per patient; 17.2% showed 4-14 different KIT resistance mutations. Of all pathogenic KIT variants, 28.0% were novel, including alterations in exons/codons previously unreported. PDGFRA mutations showed similar patterns. ctDNA-detected KIT ATP-BP mutations negatively prognosticated avapritinib activity, with a median progression-free survival (mPFS) of 1.9 versus 5.6 months for regorafenib. mPFS for regorafenib did not vary regardless of the presence or absence of ATP-BP/A-loop mutants and was greater than mPFS with avapritinib in this population. Secondary KIT ATP-BP pocket mutation variants, particularly V654A, were enriched upon disease progression with avapritinib.

CONCLUSIONS

ctDNA sequencing efficiently detects KIT/PDGFRA mutations and prognosticates outcomes in patients with TKI-resistant GIST treated with avapritinib. ctDNA analysis can be used to monitor disease progression and provide more personalized treatment.

The tropical bedbug Cimex hemipterus near the southernmost extent of its range

The average degree of infestation of Cimex hemipterus in Zulu huts in South Africa is the same as that of C. lectularius. Nymphal stages of C. hemipterus can be distinguished by head-width measurements and numbers of lateral pronotal hairs.

Changes in the relative frequency of occurrence of infestations of two sympatric species of bedbug in northern Natal and KwaZulu, South Africa

Between 1983 and 1988 the frequency of Cimex hemipterus infestations relative to C. lectularius increased near the Mozambique border and around main roads in the Nkundusi-Mfekayi area of South Africa (28 degrees 15'S; 30 degrees 23' E). In areas where both species were common, the observed number of doubly-infested huts equalled the expected. A hut infested by both bedbug species showed a significant change to a higher proportion of C. hemipterus in the adult population over 2 months. The general increase in C. hemipterus is thought to be due to the large influx of migrants into South Africa in recent years.

Production of a hybrid between the bedbugs Cimex hemipterus and Cimex lectularius

Of 479 eggs laid by female Cimex lectularius Linnaeus and C.hemipterus (Fabricius) mated by males of the other species, one was fertile and gave rise to a first stage nymph. The egg showed sculpturing typical of C.hemipterus, the female parent, and the nymph conformed to the narrow pronotum and abdomen of this species, being significantly different from C.lectularius in the width of the abdomen. Because the orientation and lengths of the bristles on the sides of the abdomen were distinctly different from C.hemipterus and closely resembled C.lectularius, the single nymph obtained from the cross C.hemipterus x lectularius was interpreted as being a hybrid rather than a product of parthenogenesis.

The occurrence of the bedbugs Cimex hemipterus and Cimex lectularius in northern Natal and KwaZulu, South Africa

Two species of anthropophilic bedbugs, Cimex lectularius and C. hemipterus, infest dwellings in KwaZulu, the known range of the latter extending to 28 degrees 15'S. C. hemipterus is the more common species in KwaZulu north of 27 degrees 15'. The pattern of distribution of C. hemipterus in South Africa is consistent with the species requiring a tropical climate, being a more recent invader than C. lectularius, and being able to thrive sympatrically with the latter species.

The common bedbug Cimex lectularius in African huts

The size and life-stage structure of heavy infestations of C. lectularius in Zulu huts were determined. The presence of more than one person in a hut at night, and control measures attempted by hut owners were found not to influence bedbug numbers significantly.

A preliminary investigation of the effect of age, sex and time of collection on the feeding patterns of Glossina morsitans morsitans Westw. in Zambia

Glossina morsitans morsitans were collected during the dry season of 1975 from two areas in the Luangwa Valley (Zambia) and from one of the areas in the wet season of 1976. In all, 1,190 flies were analysed for sex, wing fray category and source of bloodmeal. Differences in the feeding patterns in the morning and afternoon collections reflected host behaviour. Warthog consistently emerged as a major host but there appeared to be some local variation resulting from seasonal and diurnal availability of hosts.